Catalytic treatment of hydrocarbons



' AU@ 5, l94,1- F. A. HOWARD 2,251,571

CATALYTIC TREATMENT 0F HYDROCARBONS Filed Nov. 19, 1937 ZZ 5I fz 2a 1www Patented 1941 OFFICE f CATALYTIC TREATMENT! 0F HYDE@- t CABBONS FrmA. nowara'auubeta; N. r., signor t@ Standard Oil Development ompany, acorporation or Delaware Application November l 8 Claims.

The present invention relates to the catalytic ltreatment oihydrocarbons and particularly to endothermc treatments such as crackingand dehydrogenation.

One ot the major dimculties encountered in catalytic cracking anddehydrogenation is the maintenance of an optimum temperature throughoutthe catalytic mass The difiiculty has been that when enough catalyst isemployed 4to provide a proper time of contact for the desired conversionof the hydrocarbons, by reason of the endothermiq nature of thereaction, the temperature of the hydrocarbons is rapidly diminished inits passage through thr` catalytic mass so that it is not in contactwith the catalyst at the proper temperature for the whole time of itspassage therethrough. If it be attempted to supply enough heat to thefeed stock as preheat to keep the temperature within an optimum rangethroughout the entire catalyst mass, cracking to an undesirable extentoccurs in the preheater and mre especially in the pipe connecting thepreheater with the reaction chamber.

This has led to the practice of mixing the hydrocarbon feedstock withinert gas or vapor such as steam which can pass through thel catalyticbed without suii'ering any loss of heat other thanthat due to radiation,which loss lslargely eliminated by suitable insulation of the reactionchamber. The obvious drawback to this procedure is that it cuts down thecapacity of the unit and requires the employment of a special procedurefor the recovery of the products from inert gas.

According to the present invention, hydrocarbons, particularly those ofnormally liquid nature such as gas oils, are cracked or dehydrogenatedby being preheated to a cracking temperature or thereabouts, and passedthrough a catalyst chamber to which is fed at suitably spaced pointsother hydrocarbons of greater therm'al stability against decompositionheated to a, temperature above the optimum cracking temperature of s aidfirst mentioned hydrocarbons. In general, for hydrocarbons of the sametype, such as saturated hydrocarbons or olei'ins, the thermal stabilityagainst lcracking decomposition var es inversely with the molecularweight. In

`i other words, the lower the molecular weight,l the greater thestability. Moreover, saturated hydrocarbons are, in general, more stablethan the corresponding oleilns. The hydrocarbons employed for themaintenance of the reaction temperature in accordance with my invention,are those of a materially lower molecular weight 9,- fi937,.Seriailda75,359 (er. ies-it)v than the hydrocarbons undergoing reaction. For

example, when converting gas oils, normally gaseous hydrocarbons, suchas butane, propane, ethane, methane and corresponding oledns may beemployed. Likewise, light normally liquid hydrocarbons, such as thepentanes, hexanes and corresponding olens may be employed. .Any

hydrocarbonwhich has the requisite thermal stability may be utilized.Although these light 'hydrocarbons are relatively stable against thermaldecomposition under temperature conditions for cracking of the heavieroils constituting the main charging stock, they nevertheless have amarked iniiuence on the yield and character of -l the gasolineproduced.` While the exact cause has not been fully established, thereis reason to believe that a portionv of the light hydrocarbons combinewith the oleiins and aromatic products resulting from cracking theheavier oil.

In the preferred embodiment or the present invention the cracking ordehydrogenation catalyst is arranged on spaced trays in the reactionchamber which is highly insulated. The hydrocarbon feed stock. afterpassing through a preheater is fed into the reaction chamber above thetop tray. The hydrocarbons employed for temperature maintenance areintroduced into the reaction chamber between the trays.k Thisarrangement makes it lpossible to accurately control the catalysttemperature. 'Itis not necessary to arrange the catalyst in this mannerin order to secure the advantages oi the present invention. The catalystmay also be employed in the form of a deep bed in which are arranged atspaced points inlets for the superheated'hydrocarbons utilized for themaintenance of the reaction temperature.

The catalyst to be employed in the reaction chamber will depend upon thereaction desired. For dehydrogenation, any well' known. dehydrogenationcatalyst may be employed. Examples of these are metals of group 6 of theperiodic system and their compounds, particularly the oxides `andsulphides thereof, and combinations of these substances with metals, orcompounds thereof, of other groups of the periodic system,

such as groups 2 and 4.

I'he process of the present invention is more particularly applicable tothe catalytic cracking of relatively high boiling hydrocarbons, since inthis operation it is possible to use the higher pressures whichaccelerate the reaction between unsaturated compounds produced by thecracking of said hydrocarbons and low boiling or nor- 55 mally gaseoushydrocarbons utilized for the maintenance of the reaction temperature.'I'he catalyst best suited for this cracking operation is a clay,particularly one of bentonitic character, which has been activated bytreatment with a mineral acid. Catalysts which accelerate cracking maybe associated with the clay. Among these may be mentioned metals of theiron group and their compounds, especially nickel and itsA compounds. Itis of especial advantage to employ a clay containing an acid, such asphosphoric acid. A particularly suitable catalyst is one prepared byabsorbing a metal halide such as aluminium chloride on an adsorbentsupport such as silica gel. When this vtype of catalyst is employed, itis advantageous lto introduce chlorine into the reaction chamber withthe feed stock or with thei auxiliary hydrocarbons used for temperaturemaintenance.

The temperature employed for the, catalytic cracking of liquidhydrocarbons will vary with the boilingvpoint range of the feed stock.In general, it will be above about 700 F. and not higher A than about900 F. For gas oil, a preferred operating temperature lies between 800F. and 900 F. With a higher boiling feed stock the temperaturewill besomewhat lower within the broad range specified unless the feed stock isespecially refractory.

The process may be carried out at atmospheric or moderatesuperatmospheric pressure.

In its preferred embodiment the process of the present inventionincludes the separation of the total reaction products into normallyliquid constituents, which may be restricted to those having 6 or morecarbon atoms, an intermediate fraction preferably containing Ca to Chydrocarbons,

which may in some instances include Cz hydrocarbons if the latter arecomposed mainly of ethylene, and a normally gaseous fraction composed ofhydrogen, methane. and usually, ethane. The normally gaseous fractionand the normally liquid fraction are removed from the system while theintermediate fraction is recycled to the catalyst chamber. In lieu ofpassing the total intermediate fraction to the catalyst chamber, thisfraction may be first subjected to polymerizing treatment to polymerizereadily polymerizable oleflnic constituents, such as the butylenes which'are relatively unstable thermally as compared with other hydrocarbonsof similar boiling range. 'I'he polymerizing treatment may beaccomplished by any of the methods well known in the art, such as, forexample, in the presence of a catalyst such as sulphuric or phosphoricacid. v

The process of thepresent invention will be better understood from thefollowing detailed description thereof in conjunction with the apparatusshown in the accompanying drawing, in which the single figure is a frontelevation, partly in section, of one form of apparatus which may beemployed.

Referring to the drawing in detail, I designates i a reaction chamberprovided with trays 2 on which are arranged beds of catalytic-material3.

Normally liquid hydrocarbon feed stock to be cracked or dehydrogenatedis introduced into the system through feed line 4 and passed throughhydrocarbons. Each of pipes B terminates inside the reactor in adistributing head I 0 which may be of any desired type. VArranged infeed line 3 is a heater I I.

When the catalyst has lost its activity it is regenerated by burning offthe carbonaceous material deposited thereon. This is accomplished bypassing a: stream of air, preferably diluted with steam or an inert gas,through the catalyst at a temperature of about l000 F. suitable for thecombustion of the carbonaceous material. The regenerating medium may beintroduced to the reaction chamber through line I2 connecting with line,4 and the products of regeneration removed through line I4 branchingfrom line 6.

It is advantageous to provide bailles between the catalyst beds 2 inorder to insure a thorough and uniform mixing of the heating medium andthe reaction material.- These baiiies may take the form of annularplates I6 and I1v spaced from 'each other with a central circular plateI8 beer materials pass off at the top through line 25..

It is to be understood that fractionator 22 may be so operated that onlyhydrocarbons boiling above the gasoline range are withdrawn at thebottom, gasoline is withdrawn as a side stream and lighter hydrocarbonsare taken off at the top, When operated as illustrated, the liquidproducts withdrawn through line 23 are separated into gasoline and arecycle stock.

Line 25 is provided with a branch line 26, controlled by a valve 21,through which the hydrocarbon mixture carried oif from fractionator 22`may be introduced between the plates of a second fractionator 28 whichis suitably refrigerated to cause the condensation of propaneand higherhydrocarbons. Fractionator 28 is provided with a liquid 'drawoff line 29connected with line 9 and controlled by a valve 30 and a gas drawofl.line 3|. Line 25 is connected with line 29 below valve 30 in order thatthe fractionator may be bypassed in the event that the composition ofthe light fraction recovered from fractionator 22 is suitable forrecycling without fractionation.

As before mentioned, the recycle gas may be first subjected topolymerization treatment to polymerize readily polymerizableconstituents such as butylenes before being returned to the catalyticchamber. To this end, the return line 29 is providedv with a valve 32and with a branch line 33 leading to a suitable polymerizing unit. Forpurpose of illustration, there is shown a polymerizing unit employingsulphuric acid as a catalyst, it being understood that other types ofpolymerizing units may be employed. i

With valve 32 closed and valve 34 in branch line 33 open,the recyclestock passes through line 33 to a polymerization chamber 35 to whichsulphuric acid catalyst may be fed through line 33 so as to pass throughchamber 35 concurrently with the recycle stock. It is to be understoodthat feed line 36 may be provided with a dispersing tom of whichacid iswithdrawn through line I9A and from the upper end of which hydrocarbonsare withdrawn through line 40 and discharged into a separator 4I heldunder conditions suitable for the condensation of Cs and higherhydrocarbons which are lwithdrawn from the bottom thereof through lineIZ. The remainder ofthe recycle stock is conducted from separator l4Iback to line 29 through line d3.

It is apparent that many changes can be made in the process abovedescribed without departing from the scope of the present invention. No

attempt has been made to indicate in the drawing the various points atwhich heat exchangers may be advantageously employed. It may bementioned that considerable heat conservation may be realized byeffecting heat exchange between the outlet or reaction chamber i andrecycle feed line 29. In addition, as previously stated, the catalystmay be arranged in a single bed of considerable depth and the reactionmaterial and the heating mixture introduced into the bed vthroughsuitably arranged tubes. It is to be understood also that a plurality ofreactors will be employed, with one or more reactors on regenerationwhile the others are on stream. In such an arrangement the products ofregeneration are employed to preheat the feed stock to reactors onstream, preferably being first passed into heat exchange relation withthe light hydrocarbon heating medium and then into heat exchangerelation with the heavier feed stock.

The natureand objects of the present invention having thus beendescribed and illustrated, what is claimed as new and useful'and isdesired to be secured by Letters Patent is:

l. A process for cracking liquid hydrocarbons which comprises preheatingsaid hydrocarbons substantially to the desired cracking temperature,passing the preheated hydrocarbons through a-plurality of spaced layersof a cracking catalyst contained in a reaction chamber, simultaneouslypreheating a mixture of light hydrocarbons, including hydrocarbonsranging from Ca to Cs, to

a temperature above the desired cracking temperature, introducing thepreheated light hydrocarbons into the reaction chamber at pointsVbetween adjacent layers of catalystand removing the reaction productsfrom the reaction chamber.

2. A process for cracking liquid hydrocarbons which comprises preheatingsaid hydrocarbons to substantially the desired cracking temperature,feeding the preheated hydrocarbons to a mass of cracking catalyst,removing the reaction products from the catalytic mass, recovering from-the reaction product a fraction boiling within the gasoline range and aseparate fraction including Ca to Cs saturated and unsaturatedhydrocarbons, subjecting the latter fraction to a treatment suitable for the removal therefrom of unsaturated hydrocarbons, heating theresidual light fraction to a temperature above the desired crackingtemperature and feeding the heated light hydrocarbons to the catalyticmass together with the initial material.

3. A process, according to the preceding claim,

in which the unsaturated light hydrocarbons are 4removedbypolymerization by the action of an acid polymerizin'g agent.

4. A process for cracking liquid hydrocarbons to produce hydrocarbonsboiling within the gasoline range which comprises preheating saidhydrocarbons substantially to the desired cracking temperature, feedingthe preheated hydrocarbons to a granular mass of cracking catalystmaintained at the desired reaction temperature, removing the reactionproducts from the catalyst mass, dividing the reaction product into afraction containing only hydrocarbons boiling .at least in the gasolinerange, a fracti'on composed mainly of Ca to Cs hydrocarbons and alighter :traction mainly composed of permanent gases,

heating the intermediate fraction to a temperature above the desiredcracking temperature but below the temperature at which any substantialdecomposition of the intermediate fraction occurs and feeding the heatedintermediate fraction into said reaction zone and into the catalyst atspaced points alon'g the length of said reaction zone to supply heat tosaid reaction zone without supplying heat by indirect heat exchange.

5. A process, according to the preceding claim, in which the catalyticmass employed is a clay containing phosphoric acid.

6. A process for cracking normally liquid hydrocarbons to produce motorfuels which comprises heating said hydrocarbons substantially to acracking temperature, passing the heated hydrocarbons through aplurality of spacedbeds of granular cracking catalyst contained in areaction chamber, introducing a mixture of heated relatively lighthydrocarbons into said reaction chamber at points between certainadjacent beds of catalyst to supply additional heat to the normallyliquid hydrocarbons'undergoingl cracking and to maintain them atcracking temperature, the 'light hydrocarbons consisting essentially ofC: to C5 hydrocarbons and being heated to a higher temperature than thecracking temperature for the normally liquid hydrocarbons but below thetemperature at which any Asubstantial (decomposition of the lighthydrocarbons occurs tially of Ca to C5 hydrocarbons and Ahaving a yhigher thermal stability than the normally liquid hydrocarbons,introducing the preheated light hydrocarbons into the catalyst mass atspaced points alongthe path of travel of the normally liquidhydrocarbons therethrough to supply heat lost during the-conversion asthe normally liquid hydrocarbons pass therethrough and to maintain thedesired extent of conversion without supplying heat by indirect heatexchange, removing the reaction products from the catalyst mass andrecovering therefrom a hydrocarbon mixture boiling within the gasolinerange.

8. A process for cracking hydrocarbons which comprises preheating arelatively heavy hydrocarbon oil substantially to the desired crackingtemperature, passing the preheated hydrocarbon oil through a relativelylarge granular mass of particles of a cracking catalyst in a reactionchamber, providing a mixture of light hydrocarbons consistingessentially of C3 to C5 hydrocarbons and having a higher thermalstability than the normally liquid hydrocarbons, separately heating thelight hydrocarbons to a temperature above the desired crackingtemperature for the 10

